On the way home today was only making 12.6 V so I shut it off and re-started it and it went right to 13.6v. Ride home was smooth and fine so I think it is voltage related.
And the tyres were cold and I get a bit of dirt cause I had to "top" my drive way to get clearance (literally had to rip the concrete crown off the top of the driveway!). Oh and my GTR is a pretty serious rebuild, forged internals, tomei cams and N1 turbos. Hehe, it does have some get up and go so that's prob why more like your friends hitting nearly 50% at not probs. And that is on Yoko A048's!